With increasingly strict requirement of national energy efficiency index, the existing two-stage enthalpy-increasing compressors solve the problem of insufficient heating capacity at low temperatures by air supplying and enthalpy increasing, thereby increasing heating capacity of an air-conditioning system.
A two-stage enthalpy-increasing compressor in the prior art comprises one secondary cylinder and two primary cylinders that supply air to the secondary cylinder. Under a heavy load working condition (e.g., nominal refrigeration, nominal heating, national standard working condition, low-temperature working condition, etc.), in the case of a relative large pressure ratio, two-stage compression may effectively allocate the pressure ratio, such that the primary-stage cylinder and the secondary-stage cylinder can operate efficiently. However, under a low load working condition (e.g., IPLV working condition, intermediate working condition, etc.), in the case of a relatively lower pressure ratio, pressure-ratio allocation by two-stage compression will be less efficient, which easily causes a too small pressure ratio allocated to the first-stage cylinder or the secondary-stage cylinder; at this point, the cylinder essentially becomes one resistive component with a gas exhaust valve disc, thereby reducing compressor energy efficiency.
Due to not having a single-stage working mode, the two-stage compressor in the prior art cannot switch between the two-stage working mode and the single-stage working mode, resulting in a low energy-efficiency of the compressor in a low load working condition.